Rotogravure is an industrial printing technique that is particularly in use for the printing of materials in high quantities, wherein the printed design is unchanged for a certain period. A properly manufactured cylinder can be resurfaced dozens, if not hundreds of times over the useful life of a cylinder (which in some cases can be as much as 25 years or more); each time at a fraction of the cost to manufacture a new cylinder. Moreover, the high quality of the print generated off of an imaged surface of a rotogravure cylinder is a major advantage over other printing techniques. A further advantage of rotogravure cylinders is the ability to resurface the worn or obsolete imaged copper layer.
Rotogravure is for instance used for printing of packaging materials, but also book covers. The rotogravure cylinder is rotated at high speed during printing. Typically after a substrate has been printed by means of a first cylinder, it will be printed again with a second rotogravure cylinder. Each cylinder is herein provided with the pattern for one specific color ink. The total print is then built up from the overlapping patterns of the different color inks.
In view of the high speed of rotation and the regular exchange of cylinders, printing machines (hereinafter also referred to as printing presses) are provided with a first shaft for holding and rotating the cylinder. Since the cylinders are usually hollow, they are provided with end plates, each with a connection area for the shaft. Such connection area is for instance an aperture fitting for the shaft. Traditionally, the end plates (also known as steel flanges) are permanently fitted into the rotogravure cylinders. A rotogravure cylinder is “set” by mounting the cylinder's steel flange ends into or unto protruding shafts. The steel flanges are sized and shaped to allow a rotogravure cylinder to be set on a printing press. The steel flanges produce significant support across the length of the cylinder during press runs and therewith allow production of high-quality images.
The end plates may be attached to the cylinder by means of pressing the end plates into the bore of the cylinder, or alternatively by means of mechanical attachment. One such mechanical attachment is known from U.S. Pat. No. 3,294,889. In said known system the shaft—just one—is also part of the cylinder. Another embodiment is known from EP0038385. These end plates are quite important, since they are responsible for transmission of the power from the shaft to the surface area. Moreover, any space between the shaft and the end plate will translate itself into mistakes with the printing, i.e. it would easily lead to misalignment between the various cylinders each transferring a pattern to the substrate that jointly forms the desired image.
For a variety of reasons, different printing presses from the same of different manufacturers have non-standard shaft dimensions. Consequently, when receiving an order to manufacture a new cylinder, the manufacturer must also be provided with the exact shaft size dimensions the cylinder is to be mounted on so as to attach the necessary flanges to the cylinder so it can be used on the desired printing press.
Traditionally, the cylinders comprise a base of steel at the outside of which a plurality of layers is deposited. These layers typically comprise an adhesion layer, a support layer, an engraving layer and normally a chromium-based protection layer. In order to attach the end plates use may be made of pressing the end plates into the bore, and more particularly clamping of those end plates. This is a permanent fitting of the steel flange of an end plate into the rotogravure cylinder. Over time, printer facilities tend to amass a large stock of rotogravure cylinders for possible future resurfacing. The high investment cost to have a cylinder produced and shipped to the printer in the first place is a deterrent to recycling, as is the fact that accommodations must be made to have heavy steel cylinders transported for recycling. Also, recycled cylinder is not a high value commodity which means there is little return revenue generated from recycling.
All in all, most printer facilities elect to keep (store) used cylinders with the expectation that a cylinder's specifications (including insert dimensions) may match the need to place an order for a new cylinder. When this occurs, resurfacing an existing cylinder is often a lower cost option than ordering a new one. Recently, improvements have been made to make rotogravure cylinders less heavy and allowing resurfacing. However, one of the initial and key elements of resurfacing involves loading the insert ends of the cylinder onto an apparatus which is used to remove the engraved copper layer by machining. The machining process completely removes the old image and prepares the cylinder for copper re-plating after which a new image will be etched using conventional means. When necessary or prudent, the entire copper layer is removed down to the original base.
Some printer facilities are able to in-house manufacture gravure cylinders. However, this is not the norm. Most printer facilities have cylinders manufactured off-site, which means that any resurfacing involves sending a stocked cylinder to a remote site where it is machined, re-plated and re-imaged, and generally also re-chromed. Re-chroming involves bathing the re-imaged layer in chrome (usually a hexalent-chrome bath solution, which is quite toxic to the environment in natural form and thus must be contained and handled in a manner which adds to the cost of cylinder production). The very use of chrome plating in gravure cylinder production and the significant weight attribute of cylinders being made of steel (which can be a difficult handling and transportation problem, particularly in countries or regions of the world where weight restrictions are taken seriously), has driven many printers to search for alternatives to gravure printing, driving down demand for gravure cylinder production. The transition to different printing approaches, including flexographic and digital printing in some cases, by way of example, over time is believed to have discouraged R&D activities aimed at trying to come up with solutions on making gravure cylinders and gravure printing better, cheaper, and more commercially competitive than alternate technologies.
Improved gravure cylinder configurations that address the above challenges with gravure printing, and restore demand for the high(er) quality nature of gravure printing is greatly desired by the industry.